Half way up Mauna Kea on the saddle road crossing the big island of Hawaii there is a trail to the south of the road. 5 miles down that trail to the right is a Puka (Hawaiian for lava hole) about 100 feet around and 3o feet deep. This is the main entrance to the Emerson Lava Tube. This lava tube is nearly a mile long and a great hike. Bring boots, flashlights and a helmet is nice. Don’t forget sunscreen for the hike out. It’s sunny and at nearly 8,000 feet in elevation.